Abstract
BackgroundOverconsumption of energy from food contributes to high rates of overweight and obesity in many populations. A promising set of interventions tested in pilot studies in worksite cafeterias, suggests energy intake may be reduced by increasing the proportion of healthier – i.e. lower energy – food options available, and decreasing portion sizes. The current study aims to assess the impact on energy purchased of i. increasing the proportion of lower energy options available; ii. combining this with reducing portion sizes, in a full trial.MethodsA stepped-wedge randomised controlled trial in 19 worksite cafeterias, where the proportion of lower energy options available in targeted food categories (including main meals, snacks, and cold drinks) will be increased; and combined with reduced portion sizes. The primary outcome is total energy (kcal) purchased from targeted food categories using a pooled estimate across all sites. Follow-up analyses will test whether the impact on energy purchased varies according to the extent of intervention implementation.DiscussionThis study will provide the most reliable estimate to date of the effect sizes of two promising interventions for reducing energy purchased in worksite cafeterias.Trial registrationThe study was prospectively registered on ISRCTN (date: 24.05.19; TRN: ISRCTN87225572; doi: https://doi.org/10.1186/ISRCTN87225572).
Highlights
MethodsA stepped-wedge randomised controlled trial in 19 worksite cafeterias, where the proportion of lower energy options available in targeted food categories (including main meals, snacks, and cold drinks) will be increased; and combined with reduced portion sizes
Overconsumption of energy from food contributes to high rates of overweight and obesity in many populations
A Reynolds et al BMC Public Health (2019) 19:1611 series of pilot studies were conducted to assess the impact on energy purchased in worksite cafeterias of these three interventions [15], a important environment to target for interventions as an estimated 11– 18% of an adult’s meals occur while at work [16]
Summary
Study design A stepped-wedge design (Campbell & Walters, 2014) will be used, with each of the 19 sites randomly allocated to the time at which they implement each of the two interventions across a period of 25 weeks (see Additional file 2). We selected a one-sided test, reflecting existing evidence This includes previous worksite studies of the same interventions to be evaluated in the current study – Availability and Size [17, 18] – in which there were reductions in 11 of 12 cafeterias using the same primary outcome as will be used in the current study – i.e. energy purchased in intervention categories. The pre-specified threshold for intervention adherence (i.e. proportion of less healthy items offered for Availability) within each intervention category is defined in Additional file 1, with at least a 10% reduction by volume in each targeted product required for Size. Due to the nature of the stepped-wedge design it will not be possible to blind the statistician to intervention status while conducting the analysis
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